The present invention relates to a vehicle seat and, more particularly, to a vehicle seat configured so as to reduce a shock at the time of rear-end collision.
Generally, in a so-called rear-end collision, in which the rear part of a vehicle, such as an automobile, is struck from behind, or collides heavily when running backward, the head of a passenger on a vehicle seat is tilted to the rear suddenly by an inertial force, and the neck of the passenger may get a shock.
Therefore, conventionally, the seat for a vehicle such as an automobile is provided with a headrest, which supports the passenger's head, above a seat back to protect the passenger's head and neck from a shock caused by rear-end collision and to reduce the shock to the neck.
However, if the headrest is merely provided, the shock to the passenger's body cannot be reduced, and also, in some cases, the shock applied to the neck cannot be reduced sufficiently unless a gap between the passenger's head and the headrest is decreased quickly when a rear-end collision occurs.
To solve the above-described problems, there has been disclosed a technique in which in a vehicle seat provided with a seat back in which a seat back cushion is supported by a seat back frame, an abutting part of the seat back on which the back part of the passenger abuts in rear-end collision has a spring coefficient smaller than that of other parts and a damping coefficient larger than that of other parts (for example, refer to Japanese Unexamined Patent Application Publication No. 2005-028956 (“the '956 Publication”)).
Also, there has been proposed a vehicle seat in which in a seat back having a headrest, a movable frame having a spring body for supporting a cushion material is attached to a fixed frame to which the headrest is mounted in an upper part so that the upper part of the movable frame rotates to the rear around the lower part thereof, and between the fixed frame and the movable frame is provided a spring that carries a usual seating load, but permits the movable frame to rotate rearward when an impact load not lower than a predetermined value is applied (refer to Japanese Unexamined Patent Application Publication No. 2000-272395 (“the '395 Publication”)).
Further, there has been known a technique in which both of the right and left sides of a headrest mounting rod are attached to a seat back frame via an upper side link for moving the headrest back and forth (refer to Japanese Unexamined Patent Application Publication No. 2007-062522 (“the '522 Publication”)).
The technique disclosed in the '956 Publication aims to ease the shock to the passenger. In the technique disclosed this publication, by decreasing the spring coefficient of the abutting part of seat back on which the back part (“the chest part” in this publication) of the passenger abuts, the rearward displacement of the upper body is increased, and the relative displacement of the head with respect to the back part is decreased. Also, by increasing the damping coefficient by using a low resilience cushion material, the rebound of the upper body is restrained to decrease the relative speed of the head with respect to the back part. Thereby, a shearing force acting on the neck is decreased.
Unfortunately, the technique in which the spring coefficient is decreased and the technique in which the low resilience cushion material is used have a disadvantage that the sinking of the body to the vehicle rear cannot be increased (that is, the displacement cannot be increased).
Also, the technique disclosed in the '395 Publication has an advantage that a working load for rearward movement of a central support part can be predicted certainly with only setting an elasticity of spring respect to the impact load, the central support part always moves rearward, and the operation is certain.
However, the technique disclosed in this publication has a disadvantage that the movability of the movable frame with respect to the fixed frame near the lower part position is very poor, so that all of the seated body cannot sink to the rear side of vehicle because the fixed frame and the movable frame are fixed to each other by a mounting shaft in the lower part. Also, the spring of this publication has a problem in that the spring is made difficult to move by a reaction force that becomes high as the spring moves significantly, and also the movable range of the movable frame with respect to the fixed frame is extremely limited, so that it is difficult to secure displacement that sinks the body significantly. Since the movable frame is used, the apparatus increases in size as a whole, and therefore this technique also has a disadvantage that it is difficult to reduce the weight.
Further, the technique disclosed in the '522 Publication is a technique in which for the upper side link, one end (rear end) of a first link rod that is a part of the upper side link is attached to a movable-side bracket fixed to both of the right and left ends of the headrest mounting rod by a shaft, the other end of the first link rod is rotatably attached to a fixed-side bracket provided above both of the right and left sides of the seat back frame by a shaft, one end of a second link rod is pivotally mounted to the movable-side bracket below the first link rod by a shaft, the middle part of the second link rod is rotatably attached to the fixed-side bracket by a shaft, and further a plate body is attached so as to be movable back and forth via wire springs provided in parallel with each other in the up and down direction. In this technique, the tip end of a mounting end part on both of the right and left sides of the wire spring is positioned in front of the plate body in a plan view, so that a large space in which the cushion material can be installed can be provided between the tip end of the mounting end part and the plate body, and the cushioning performance can be improved.
In the technique disclosed in this publication, however, in order to make the headrest rotatable in a predetermined range, an inhibition part for regulating the rotating must be provided on the link rod and the like constituting the upper side link. Also, in the technique disclosed in this publication, the other end of the spring (one end of which is locked to the seat back frame side) is locked to the lower part of the first link rod, and a return spring for urging the upper side link is disposed so that the headrest is always positioned on the rear side. Therefore, if the diameter of the seat back frame is increased by the presence of the back return spring arranged above, the presence of the spring becomes a hindrance, so that the degree of freedom in designing is hindered.
Thus, a link mechanism is formed by using many members including the upper side link consisting of the plurality of link bars. Therefore, this technique has a disadvantage that not only the number of parts increases, but also the link itself increases in size.
In the techniques disclosed in that publications discussed above, a way to transmit the impact load to the headrest is needed. Therefore, these techniques have a problem in that the decrease in size and weight cannot be achieved because the configuration is intricate and has an increased size.
Also, in a technique in which a pressure receiving member is attached to the seat frame using the wire to move the headrest, the posture is held by the pressure receiving member, and the headrest is moved by a load created in the pressure receiving member, so that the deformation of a wire serving as a connecting member must be prevented as far as possible. Since the wire is not deformed, the sinking amount is hindered. Therefore, this technique has a disadvantage that it is difficult to increase the displacement, and the coexistence with a normal seating feeling is difficult to achieve.
Further, there has been known a link mechanism in which the position of a link member before operation is maintained by the installation of a spring on the link mechanism, and after operation, the link member returns to the original position.
Unfortunately, in the technique in which the position of the link member is held by using the spring, at the time of operation, in a case where the shaft center of the link member laps on the line connecting both ends of spring, even if the spring is going to return to the original state, the operation shaft does not always rotate to the return direction, and therefore may get stuck and become immovable.